1. Technical Field
This invention generally relates to a method of identifying a plurality of devices bearing identification numbers. The invention finds particular, though not exclusive, application in identifying individual ones of a plurality of electrical devices, such as sensors.
2. Related Art
A room, building, factory or other industrial plant may be provided with a plurality of electrical devices such as sensors, which devices may be controlled from a central location. For example, a large number of fire detectors may be distributed throughout an oil refinery. Such devices may be similar to each other, may be programmed to an identical default state so that detectors of the same type will leave the factory with a common default configuration (apart from their serial numbers), and yet (some at least) may need to be configured differently from each other. During manufacture, the devices are usually programmed with a unique serial number, there may be a very large quantity of such devices, differing only from one another by their serial numbers, all of which are of the same format. Any one operator could be expected to have a selection of such devices, perhaps of random serial numbers, or the devices may be connected at random into a detection system or an initially-ordered system may be disturbed in time by replacements. At any one time, therefore, the operator may have a quantity of devices whose actual serial numbers he may not know. When such a collection of devices is linked together by a common communications link from a central control station, it thus becomes very difficult to determine which serial numbers are available and with, for example electronically interrogating, which devices they are associated.
It is known to identify serial numbers and to associate them with respective electrical devices by dealing with the devices individually, for example by electronically interrogating the devices separate from the central control station, or by attaching one device at a time.
There is currently no practical method for an operator automatically to identify, maintain and enable hardware to communicate with multiple devices, all programmed to an identical default state, and all driven together from a common communications bus line. It is desirable that each unit be separately individually programmed with a user friendly unique ‘address’ code before connection to the common bus to enable data transfer to only the desired units. An address code is also preferable as less data bits will be required to communicate with the devices. This simplifies management of a system with many such devices.
A common method is to use the serial number as the identifying value. Mass produced devices must each have a long serial number to allow identification of each one over the life cycle of the product range, which can typically run into the tens to hundreds of millions. A significant overhead is needed to future proof the product. Hence, the serial number can run to many digits. On a typical system with different types of devices, some replaced, some as part of an extension, the serial numbers will become fragmented. These factors together result with an impractical way for an operator to identify and maintain a network of many of these devices.
It is also known to arrange for each device in turn to “break” the communications link and to “reattach” the connection to the next device when its serial number has been identified. However, this method requires the devices to be provided with hardware specifically for this purpose, becoming redundant once the identification and subsequent configuration has been effected. This results not only in an undesirable additional expense for the device, but also complication of the design and installation of the communications link.
It is also known to “scan” all the devices for each possible serial number from the known totality, or range, of serial numbers. A “scan” is understood to be the operation whereby a set of queries (master messages) is sent out by a control panel, each commanding that only the device with the matching serial number must reply (slave message). However, due to mass production, there may be a very large number of possible serial numbers that need to be scanned until a match is found, so the scanning could require an unacceptable amount of time to complete. Even though it is possible to arrange for there to be a delay in the sending of a matched identification signal back to the control panel to avoid a plurality of such messages colliding and disrupting the scanning, the quantity of possible serial numbers, together with the required tolerance of the timer within each device, still makes this approach too time consuming, and thus impractical.